Dynamic headspace enrichment/reinjection for open tubular GC/FTIR analysis of volatiles in polymers

An analytical system for the analysis of volatiles entrained in polymers is described. This system is based on a thermal desorption oven connected to a cold trap. After enrichment of headspace vapor, trapped material is reinjected and analyzed by open tubular gas chromatography/Fourier transform infrared spectroscopy, OTGC/FTIR. The thermal desorption oven is designed to provide different modes of sample introduction: use of a pyroprobe; insertion of a piece of quartz tubing with applied sample; or syringe injection. Headspace enrichment is carried out in a piece of fused silica capillary tubing filled with glass beads. The trap may be cooled either electrically using Peltier elements or with liquid nitrogen. A six-port rotary valve is used for flow switching between enrichment and reinjection modes. All system parameters, temperatures, and timed events, are controlled from the gas chromatograph. Dynamic headspace analysis is demonstrated as a method for polymer characterization.     

Sample enrichment in high speed narrow bore capillary gas chromatography

Reduction of the column diameter has proved to be a highly efficient tool to increase the speed of analysis. Unfortunately, the requirements for instrumental design with respect to sample input band width, low dead volume interfacing, and time constants of detection and registration systems are the more critical the smaller the inside diameter. Recently we reported input band widths as low as 1 ms [1] for gaseous samples at ppm concentration levels, without any preconcentration, in a study with narrow bore columns and thermal conductivity detection. In this study a simple versatile micro on-column cold trap/thermodesorption enrichment system for narrow bore columns is introduced and evaluated. The combination of considerable sample enrichment and preservation of the compatibility of the required input band width with column dimensions is critically examined. The process of thermodesorption (reinjection) which is the most critical step, is particularly emphasized. The system consists of a short aluminum coated fused silica or metal capillary with a low mass and a low cost electrical heating. Input band widths down to 1 ms are obtained without extreme demands on electrical power (300 watt). The potential of the system is illustrated with some extremely fast separations.     

MS/MS of ions in a low pressure linear ion trap using a pulsed gas

A pulsed valve was used to increase the pressure within the trapping region of a low-pressure linear ion trap by situating the pulsed valve close to the ion trapping region. The pressure was estimated to increase from a background pressure of 3.5e–5 Torr of nitrogen to 0.49 mTorr at the center of the trap. The increased pressure allowed excitation periods to be reduced from 100 to 25 ms without suffering losses in MS/MS efficiency during dipolar excitation. The reduction in excitation period translates into an increase in the overall duty cycle of the scan.     

Evaluation of a nitrogen-cooled, electrically heated cold trap inlet for high-speed gas chromatography

Gas chromatography has the potential to be a much faster method of separation than is usually realized. If column operating conditions are optimized for speed and injection band width is minimized, some simple separations can be completed in a few seconds. A prototype cryofocusing system for producing narrow injection bands with 0.25-mm i.d. columns is described here. The gas-cooled and electrically heated inlet produces injection bands with widths of about 10-20 ms. In the present study the system is evaluated using mixtures of common organics, including alkanes, aromatics, alcohols, ketones, and chlorinated hydrocarbons. Quantitative trapping and reinjection is achieved for all tested compounds. Coefficients of variation are less than 3% for peak area and less than 0.2% for retention time. Base-line separation of simple mixture is achieved with retention times of less than 10 s. By using the cold trap inlet with a low-dead-volume detector and a high-speed electrometer, the efficiency available from commercial capillary columns can be better utilized, and retention times for some routine separations may be reduced to a few seconds.     

Analysis of volatile organic compounds in polymers by dynamic headspace and gas chromatography/mass spectrometry

An experimental method for the analysis of volatile organic compounds in polymers is described. The technique involves dynamic headspace sampling, collection, and concentration of the volatiles in a cold trap, followed by capillary column gas chromatography/mass spectometry. Flow switching is carried out by the Deans switching technique. Four technical polymers used as pharmaceutical packaging materials have been analyzed in order to demonstrate the method.     

二阶梯度升温热解吸法测定空气中的微量丙烯腈和乙腈

采用气体采样泵将空气样品的丙烯腈和乙腈吸附到吸附管中,用二阶梯度升温将吸附管中的被测物质解吸到冷阱中,再快速对冷阱升温,将冷阱中的被测物质解吸进入色谱柱进行分离,用气相色谱氢火焰检测器检测空气中的微量丙烯腈和乙腈。丙烯腈、乙腈的色谱峰面积与吸附质量的线性相关系数均大于0.995。该法对实际空气样品中丙烯腈的检出限为5μg/m3,乙腈的检出限为10μg/m3,加标回收率均大于90%。     

Coupling of ion-molecule reactions with liquid chromatography on a quadrupole ion trap mass spectrometer

We report for the first time a coupling of gas-phase ion-molecule reactions with chromatographic separations on a quadrupole ion trap mass spectrometer. The interface was accomplished by using a pulsed valve for the introduction of a volatile neutral into the ion trap. The pulsed valve controller is synchronized with the mass spectrometer software. The setup requires some minor modifications to the vacuum system of the commercial quadrupole ion trap but most of the modifications are external to the mass spectrometer. Two applications of this interface are described: differentiation between two phosphoglucose positional isomers and detection of a phosphopeptide in a peptide mixture. Both applications are using the reactivity of trimethoxyborate towards a phosphate moiety in the negative ion mode. The detection of phosphopeptides hinges on our findings that non-phosphorylated peptide anions do not react with trimethoxyborate. This LC/MS detection can be easily visualized in terms of selected reaction monitoring.     

射流式单重态氧发生器研究

单重态氧O2(a1△g)是迄今唯一能用纯化学反应高效产生的具有长寿命的亚稳激发态分子.为了考察提出的用两个O2(1△)能量汇集反应生成氧第二单重激发态O2(b1∑+g)以实现近可见短波长化学激光方案的现实性,设计和实验了一个氯流量为3～10 mmol/s的射流式单重态氧发生器(JSOG).考察了三种具有不同孔径和孔数目的喷头、氯气流量和脱水冷阱温度等对JSOG出口的O2(1△)浓度、O2(1△)分压、氯利用率及水蒸气含量的影响.发现用聚氯乙烯管作冷阱时,最佳冷阱介质温度为-140～-150℃,对此提出了O2(1△)表面脱活与脱水互相竞争的解释.在最佳条件下,可将O2(1△)气中水分压降低至4 Pa,这一结果是首次报导.     

Internal pulsed valve sample introduction on a quadrupole ion trap mass spectrometer

A pulsed valve positioned just outside the ion trap electrodes (within the vacuum chamber) has been characterized. The observed gas pulse widths and the maximum ion intensities were found to decrease as the distance between the pulsed valve and the ion trap electrodes increased. An explanation is presented within. The pulsed valve was found to impart temporal separation in ion-molecule reactions by permitting the removal of interfering neutrals. Other factors that affect the degree of temporal separation also are presented.     

Cold trap/reinjection interface for two-dimensional gas chromatography

The construction and evaluation of an interface for two-dimensional gas chromatography is described. The interface consists of commercially available components and is attachable to available gas chromatographs without any major modifications. The interface has been constructed so as to permit “heartcutting” as well as solute band concentration. Trapping is performed in a simple cold trap of fused silica. Flow switching is accomplished by Deans switching. Factors of the over-all chromatographic performance are examined.     

Automated high-speed analysis of selected organic compounds in urban air by on-line isotopic dilution cryofocusing gas chromatography/mass spectrometry

An automated environmental air monitor has been developed to measure selected organic compounds in urban air. The instrument is based on a cryofocusing-thermal desorption gas chromatographic mass spectrometry technique where the mass spectrometer is a slightly modified residual gas analyzer (RGA). The RGA was chosen as a detector because the whole system must be robust for long periods, with 24-h continuous air monitoring. RCA are extremely simple and seemed the most reliable mass spectrometers for this purpose. Moreover, because they have no physically limited ion source, contamination is considerably reduced, so maintenance intervals are longer. The gas chromatograph is equipped with a computer-controlled six-way sampling valve, with a 100-mL sampling loop and thermal desorption cold trap injector. Environmental air is enriched with an isotopically labeled internal standard in the sampling line. This internal standard is added with a validated, custom-made, permeation tube device. The “on-line” internal standard provides for high quality quantitative data because all variations in instrument sensitivity in cryofocusing or in thermal desorption efficiency are taken into account. High repetition rates (down to 5 min for a full analytical cycle) are obtained with the use of an isothermal gas chromatography program, microbore capillary column, and environmental air sampling during the gas chromatography run.     

IEX/RP二维液相色谱中弱保留组分收集模式的构建及系统评价

以十通阀和捕集柱接口形式,构建了弱阴离子交换/反相(WAX/RP)二维液相色谱分离系统.通过将第一维离子交换色谱分析中的前部集中洗脱出的弱保留组分收集后单独分析,剩余样品进一步采用二维液相色谱分析,可以有效避免第二维色谱柱对特殊样品局部集中流出导致的第二维分离超柱容量问题,提高了系统的整体分离能力.使用4种蛋白胰蛋白酶酶解后的多肽样品评价该系统,在不分流的系统中共检测到115个峰.对第一维分离的前15 min分流后得到的组分单独分析,共识别出58个峰,后续的二维分离中共得到78个峰.2种方法相比,第二种方法检测峰数增加了21个,一些低丰度的组分在弱保留组分收集后被识别.     

Tandem hollow-fiber flow field-flow fractionation

Reinjection of one ore more collected fractions of eluted samples is recognized as a useful procedure in analytical separation techniques, among which field-flow fractionation (FFF), to improve the actual separation of complex samples. Hollow-fiber flow FFF (HF5) is a micro-channel subset of flow FFF (F4), which has recently reached a performance comparable to that of standard, flat-channel F4. To further improve HF5 of complex protein samples, we present a new device and method for in-line, reinjection HF5 that we call tandem HF5 (HF5/HF5). HF5 is ideally suited for tandem operation because (1) small channel volume and low operation flow rates allow reducing dilution and volume of the collected fractions, and (2) the relaxation/focusing step that takes place between the 1st and 2nd run (refocusing) allows reestablishing the volume and concentration of the sample plug before the 2nd elution. HF5/HF5 proves particularly effective in the case of oligomeric proteins since it allows collecting and reinjecting the bands that correspond to each separated oligomeric form. This provides information on the dynamic equilibria between the different oligomers. For HF5/HF5 operations, a modified, prototype HF5 instrumentation is presented which includes a "trap" constituted of a four-port, two-way valve positioned downstream the UV detector and a collection loop. The effect of refocusing conditions on HF5/HF5 performance is investigated by varying refocusing time. With a complex protein samples such as blood serum, HF5/HF5 can improve detectability of the low abundance components since overloading effects due to high-abundance components are reduced. This is shown for serum lipoproteins: while after the 1st run high density lipoproteins (HDLs) are not separated from high-abundance serum proteins, after the 2nd run it is shown possible to separate the HDL subclasses.     

Capturing of volatiles emitted by living plants by means of thick film open tubular traps

Fused silica open tubular traps coated with a 15μm film of methyl silicone have been successfully applied to capture volatiles emitted by living plants. The atmosphere surrounding the plants is sucked through the trap where the volatiles are retained. After sampling, the trap is installed as pre-column in a multidimensional CGC system. The volatiles are thermally desorbed, reconcentrated in a cold trap and analyzed on-line on the analytical capillary column.     

热脱附/冷阱聚焦/气相色谱/质谱法卷烟香气分析

利用热脱附装置(TDS)对烟丝粉末进行快速升温,模拟卷烟燃吸过程中蒸馏区的部分反应,用冷阱收集所脱附的物质,以GC/MS对进行定性分析.成功的分离出了有机酸、饱和烃、芳香烃、烯烃以及含氮、氧杂原子的化合物等系列超过100种有机化合物,并且还发现了典型的存在于环境中的化学污染物——邻苯二甲酸二丁酯.     

GC-MS/FID测定环境空气中57种臭氧前体物

建立了GC-MS/FID测定环境空气中57种臭氧前体物的分析方法.优化三级冷阱捕集温度、三级冷阱解析温度、初始柱温、毛细管色谱柱等实验条件.优化条件为:采用硅烷化的苏玛罐采集环境空气,目标组分经三级冷阱在-180℃低温浓缩富集,80℃解析,初始柱温为15℃,结合中心切割技术,将乙烷、乙烯、乙炔、丙烷、丙烯切割至TG-B...     

柱色谱分离、气相色谱-质谱法定性分析F-T合成油中的含氧化合物

在柱色谱柱中填充100～200目的硅胶,以二甲亚砜为洗脱剂,将F-T合成油产物分离为烃类及有机含氧化合物两部分。采用气相色谱-质谱(GC-MS)对有机含氧化合物部分进行了分析,共鉴定出有机含氧化合物139种,并对其出峰规律进行了总结。     

Beam-type collisional activation of polypeptide cations that survive ion/ion electron transfer

Doubly protonated peptides that undergo an electron transfer reaction without dissociation in a linear ion trap can be subjected to beam-type collisional activation upon transfer from the linear ion trap into an adjacent mass analyzer, as demonstrated here with a hybrid triple quadrupole/linear ion trap system. The activation can be promoted by use of a DC offset difference between the ion trap used for reaction and the ion trap into which the products are injected of 12-16 V, which gives rise to energetic collisions between the transferred ions and the collision/bath gas employed in the linear ion trap used for ion/ion reactions. Such a process can be executed routinely on hybrid linear ion trap/triple quadrupole tandem mass spectrometers and is demonstrated here with several model peptides as well as a few dozen tryptic peptides. Collisional activation of the peptide precursor ions that survive electron transfer frequently provides structural information that is absent from the precursor ions that fragment spontaneously upon electron transfer. The degree to which additional structural information is obtained by collisional activation of the surviving singly charged peptide ions depends upon peptide size. Little or no additional structural information is obtained from small peptides (<8 residues) due to the high electron transfer dissociation (ETD) efficiencies noted for these peptides as well as the extensive sequence information that tends to be forthcoming from ETD of such species. Collisional activation of the surviving electron transfer products provided greatest benefit for peptides of 8-15 residues.     

An active bubble trap and debubbler for microfluidic systems

We present a novel, fully integrated microfluidic bubble trap and debubbler. The 2-layer structure, based on a PDMS valve design, utilizes a featured membrane to stop bubble progression through the device. A pneumatic chamber directly above the trap is evacuated, and the bubble is pulled out through the gas-permeable PDMS membrane. Normal device operation, including continuous flow at atmospheric pressure, is maintained during the entire trapping and debubbling process. We present a range of trap sizes, from 2 to 10 mm diameter, and can trap and remove bubbles up to 25 muL in under 3 h.     

Purification of CH3Cl from CH3I using cold trap with sealed 2,2,4-trimethylpentane for δCl measurement

A cryogenic separation method of chloromethane (CH₃Cl) from methyl iodide (CH₃I) for δ³⁷Cl measurement with isotope ratio mass spectrometer is described. A cold trap with sealed 2,2,4-trimethylpentane (TMP) as the cryogen is used in this method. CH₃Cl can be separated from CH₃I at the TMP melting point (−107 °C) based on the difference in the vapor pressure between CH₃Cl (322.6 Pa) and CH₃I (lower than 1.3 Pa) at −107 °C. After two-step separation processes, the yields of CH₃Cl purified from CH₃Cl-CH₃I mixture are 96-101%, and the difference between the δ³⁷Cl_original and δ³⁷Cl_{After separation} is from −0.06 to +0.06‰ (0.01 ± 0.04‰). These results suggest that CH₃Cl is completely separated from CH₃I with no change of δ³⁷Cl value. This method using the cold trap with sealed TMP is very safe and not harmful, because the liquid organic compound used as the cryogen is contained in the trap and does not evaporate during the separation procedure. This method is also simple and inexpensive relative to the method using a gas chromatograph.